In a typical cellular radio system, wireless terminals which are also known as mobile terminals, mobile stations and/or user equipment units communicate via a radio access network (RAN) with one or more core networks. User equipment units or simply user equipment (UE) may include mobile telephones, such as cellular telephones, and/or other processing devices with wireless communication capabilities, for example portable, pocket, handheld, laptop computers, which communicate voice and/or data with the RAN.
The RAN covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), sometimes simply referred to as base station (BS), which in some networks is also called a “NodeB” or enhanced NodeB which can be abbreviated as “eNodeB” or “eNB” in Long Term Evolution (LTE). A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station side. The base stations communicate over the air interface operating on radio frequencies with UEs within a range of the base stations.
In some versions of the RAN, several BSs are typically connected, e.g. by landlines or microwave, to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural BSs connected thereto. The RNCs are typically connected to one or more core networks. Core networks generally comprise a Mobile Switching Center (MSC) that provides circuit-switched services and a serving GPRS support node (SGSN) that provides packet-switch type services.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM), and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UTRAN, short for UMTS Terrestrial Radio Access Network, is a collective term for the NodeBs and RNCs which make up the UMTS radio access network. Thus, UTRAN is essentially a radio access network using WCDMA for user equipment units.
The Third Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM based radio access network technologies. In this regard, specifications for the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) are ongoing within 3GPP. The Evolved Universal Terrestrial Radio Access Network (E-UTRAN) comprises the Long Term Evolution (LTE) and System Architecture Evolution (SAE).
FIG. 1 is a simplified block diagram of a Long Term Evolution (LTE) RAN 100. The LTE RAN 100 is a variant of a 3GPP RAN where radio base station nodes (eNodeBs) are connected directly to a core network 130 rather than to RNC nodes. In general, in LTE the functions of a RNC node are performed by the radio base station nodes, sometimes simply referred to as base stations. Each of the radio base station nodes, in FIG. 1 eNodeBs 122-1, 122-2, . . . 122-M, communicate with UEs, e.g. UE 110-1, 110-2, 110-3, . . . 110-L, that are within their respective communication service cells. The radio base station nodes (eNodeBs) can communicate with one another through an X2 interface and with the core network 130 through S1 interfaces, as is well known to the one who is skilled in the art.
The LTE standard is based on multi-carrier based radio access schemes such as Orthogonal Frequency-Division Multiplexing (OFDM) in the downlink and Discrete Fourier Transform (DFT)—spread OFDM in the uplink. The OFDM technique distributes the data over a large number of carriers that are spaced apart at precise frequencies. This spacing provides the “orthogonality” in this technique which avoids having demodulators see frequencies other than their own. The benefits of OFDM are high spectral efficiency, resiliency to radio frequency (RF) interference, and lower multi-path distortion. The basic LTE downlink physical resource can thus be seen as a time-frequency grid as illustrated in FIG. 2A, where each resource element corresponds to one OFDM subcarrier during one OFDM symbol interval. In more detail, the LTE downlink physical resource of FIG. 2A shows subcarriers having a spacing of Δf=15 kHz and a close-up of one OFDM symbol including a cyclic prefix.
In the time domain, LTE downlink transmissions are organized into radio frames of 10 ms, each radio frame consisting of 10 equally-sized subframes of length Tsubframe=1 ms as shown in the LTE time-domain structure of FIG. 2B.
Furthermore, the resource allocation in LTE is typically described in terms of resource blocks, where a resource block corresponds to one slot (0.5 ms) in the time domain, i.e. two slots per subframe, and 12 contiguous subcarriers in the frequency domain. Resource blocks are numbered in the frequency domain, starting with zero from one end of the system bandwidth. Downlink transmissions are dynamically scheduled, i.e. in each subframe the BS transmits control information indicating to which (mobile) terminals and on which resource blocks the data is transmitted during the current downlink subframe. This control signalling is typically transmitted in the first 1, 2, 3 or 4 OFDM symbols in each subframe. A downlink system (downlink subframe) with 3 OFDM symbols as control region is illustrated in FIG. 3.
Next, a physical uplink control channel (PUCCH) is described. As implied by the name, the PUCCH carries uplink control information, e.g., hybrid-ARQ (hybrid Automatic Repeat Request), Channel Quality Indicator (CQI), ACK/NACK, etc. LTE uses hybrid-ARQ (hybrid Automatic Repeat Request), where, after receiving downlink data in a subframe, the terminal, e.g. user equipment, attempts to decode it and reports to the BS whether the decoding was successful (ACK) or not (NACK). In case of an unsuccessful decoding attempt, the BS can retransmit the erroneous data.
Uplink control signalling from the terminal to the base station may include hybrid-ARQ acknowledgements for received downlink data; terminal reports related to the downlink channel conditions, used as assistance for the downlink scheduling (also known as Channel Quality Indicator (CQI)); and/or scheduling requests, indicating that a mobile terminal needs uplink resources for uplink data transmissions.
If the mobile terminal has not been assigned an uplink resource for data transmission, the L1/L2 (Layer 2 and/or Layer 2) control information (channel-status reports, hybrid-ARQ acknowledgements, and scheduling requests) is transmitted in uplink resources (resource blocks) specifically assigned for uplink L1/L2 control information on the physical uplink control channel (PUCCH).
Different PUCCH formats are used for the different information, e.g., PUCCH Format 1a/1b are used for hybrid-ARQ feedback, PUCCH Format 2/2a/2b for reporting of channel conditions, and PUCCH Format 1 for scheduling requests.
Next, a Physical Uplink Shared Channel (PUSCH) is described. Resources for PUSCH are allocated on a sub-frame basis by the scheduler. To transmit data in the uplink, the mobile terminal, such as the previously mentioned UE, has to be assigned an uplink resource for data transmission on the Physical Uplink Shared Channel. A PUSCH resource assignment is shown in FIG. 4, in which the resources assigned to two different users are illustrated for one subframe. The middle SC-symbol in each slot is used to transmit a reference symbol. If the mobile terminal has been assigned an uplink resource for data transmission and at the same time instance has control information to transmit, it will transmit the control information together with the data on PUSCH.
In the following, the concept of carrier aggregation is explained. LTE release 8 has recently been standardized, supporting bandwidth up to 20 MHz, for example comprising the above-described subcarriers. However, in order to meet the IMT-advanced requirements, 3GPP has initiated work on LTE release 10. One of the key components of LTE release 10 is the support of bandwidth beyond 20 MHz while ensuring backward compatibility with LTE release 8. This should also include spectrum compatibility and implies that an LTE release 10 carrier, wider than 20 MHz, should be realized as a number of LTE carriers to an LTE release 8 terminal. Each such carrier can be referred to as a component carrier (CC). In particular, for early LTE release 10 deployments it can be expected that there will be a smaller number of LTE release 10-capable terminal compared to many LTE legacy terminals. Therefore, it may be necessary to assure an efficient use of a wide carrier also for legacy terminals, i.e. that it is possible to implement carriers where legacy terminals can be scheduled in all parts of the wideband LTE release 10 carrier. The straightforward way to obtain this would be by means of carrier aggregation (CA). CA implies that an LTE release 10 terminal can receive multiple CCs (component carriers), where the CCs have, or at least have the possibility to have, the same structure as a release 8 carrier. CA is illustrated in FIG. 5 having an aggregated bandwidth of 100 MHz realized by 5 component carriers.
The number of aggregated CCs as well as the bandwidth of the individual CC may be different for uplink and downlink. A symmetric configuration refers to the case where the number of CCs in downlink and uplink is the same whereas an asymmetric configuration refers to the case that the number of CCs is different. It is important to note that the number of CCs configured in a cell may be different from the number of CCs seen or used by a terminal. A terminal may, for example, support more downlink CCs than uplink CCs, even though the cell is configured with the same number of uplink and downlink CCs.
Next, uplink power control for PUSCH and PUCCH, described above, is explained. Uplink power control is used both on the PUSCH and on the PUCCH. The purpose is to ensure that the mobile terminal transmits with sufficiently high but not too high power since the later would increase the interference to other users in the network. In both cases, a parameterized open loop combined with a closed loop mechanism is used. Roughly, the open loop part is used to set a point of operation, around which the closed loop component operates. Different parameters (targets and partial compensation factors) for a user and control plane are used. For more detailed description, it is referred to section 5.1.1.1 for PUSCH power control and 5.1.2.1 for PUCCH power control of 3GPP TS 36.213, Physical Layer Procedures, e.g. Version 9.3.0 of 2010-10-03 http://www.3gpp.org/ftp/Specs/html-info/36213.htm.
To control the UEs uplink (UL) power, the eNB will use TPC (Transmission Power Control) commands which will order the UE to change its transmission power either in an accumulated or absolute fashion. In LTE release 10, the UL power control is managed per component carrier. As in release 8/9 PUSCH and PUCCH power control is separate. In LTE release 10 the PUCCH power control will only apply to the Primary Component Carrier (PCC) since this is the only UL CC configured to carry PUCCH.
Since the TPC commands do not have any ACK/NACK, the eNB cannot be sure that the commands are received by the UE, and since the UE can falsely decode the PDCCH (Physical Downlink Control Channel) and think it received a TPC command, counting the used TPC commands cannot be used to estimate a reliable current output power from the UE. Additionally, the UE also compensates its power level autonomously (based on path loss estimates), and this adjustment is not known to the eNB. For these two reasons the eNB needs to receive PHRs (Power Headroom Reports) regularly in order to make competent scheduling decisions and control the UE UL power.
In the following, the power headroom reporting is explained. In LTE release 8, the base station may configure the UE to send power headroom reports periodically or when the change in path loss exceeds a certain configurable threshold. The power headroom reports indicate how much transmission power the UE has left for a subframe I, i.e., the difference between the nominal UE maximum transmit power and the estimated required power. The reported value is in the range 40 to −23 dB, where a negative value shows that the UE did not have enough power to conduct the transmission.
The eNB uses the reported power headroom (PH) as input to the scheduler. Based on the available power headroom the scheduler will decide a suitable number of PRBs (Physical Resource Blocks) and a good MCS (Modulation and Coding Scheme) as well as a suitable transmit power adjustment (TPC command). In carrier aggregation, the eNB would make such evaluation per UL CC since power is controlled per CC according to RAN1 decisions.
Since we have UL power control per CC and separate for PUSCH and PUCCH, this will also be reflected in the power headroom reporting. For release 10 there will be two types of PH reports:                Type 1 power headroom report—computed as: P_cmax,c minus PUSCH power (P_cmax,c−P_PUSCH)        Type 2 power headroom report—computed as: P_cmax,c minus PUCCH power minus PUSCH power (P_cmax,c−P_PUCCH−P_PUSCH)        
The Secondary Component Carriers will always report Type 1 PHR since they are not configured for PUCCH. The Primary Component Carrier would report both Type 1 and Type 2 PHR. Type 1 and Type 2 PHR must be reported in the same subframe.
Applying the release 8 framework for Power Headroom Reporting to Carrier Aggregation would imply that a PHR for a specific component carrier is sent on that component carrier itself. Furthermore, a PHR may only be transmitted on a component carrier if the terminal has PUSCH resources granted on this CC.
In RAN2 (Radio Access Network 2), it is proposed to extend this framework so that PHR for one component carrier can be transmitted on another component carrier. This enables to report rapid path loss changes on one component carrier as soon as the terminal has PUSCH resources granted on any configured UL component carrier. More specifically, a path loss change by more than dl-PathlossChange dB on any component carrier triggers transmission of a PHR on any (the same or another) component carrier for which the terminal has PUSCH resources granted.
In addition to the PHR, there will be a Pcmax,c report per CC reporting the configured transmission power of the UE, which is denoted Pcmax,c in 3GPP 36.213.
The Pcmax,c report may either be included in the same MAC (Medium Access Control) control element as the PH reported for the same CC, or it may be included in a different MAC control element. Some details are specified in R1-105796 (3GPP Liaison Statement), but exact formats and rules are not defined yet.
Power headroom will in release 10 be reported for all configured and activated CCs. This means that some of the CCs reporting PH may not have a valid UL (uplink) grant in the TTI (Transmission Time Interval) where power headroom is reported. They will then use a reference format PUSCH and/or PUCCH to report a so-called virtual/reference format PH/PHR. These reference formats are described in R1-105820 (3GPP Liaison Statement). This may be useful since they may be scheduled and transmit in the future. In other words, for a so called virtual transmission, the CC is activated but it is not transmitting, however might be scheduled to transmit in the future.
Upon configuration, each CC is assigned a Cell Index which is unique for all CCs configured for a specific UE. The SIB2 (System Information Block 2) linked UL and DL are associated with the same Cell Index. The Cell Index can have a value 0-7. The Primary Cell (PCell) is always assigned the value zero.
The reporting of one or more PHs relating to one or more CCs can be done using a PH MAC control element, however, the format thereof is not defined. In particular, for reporting power headrooms as well as transmission power information, such as Pcmax,c, extra overhead may be generated leading to a waste of resources.
It is desirable to provide a vehicle, such as a control element, which allows efficient reporting of power information as well as methods, user equipments, base stations, systems and computer programs which allow to report or handle transmission power information, such as Pcmax,c, efficiently.